"I know someone has the information that could help us find Lauren. Maybe you feel it is too late to help Lauren and so why bother," Spierer wrote. "What you might not be considering is the heartache your lack of action has caused our family and friends. The not knowing is almost unbearable."

Spierer continued to write that she had been told those who have information about her daughter's disappearance have failed to come forward because they might be afraid of getting into trouble, or were afraid "of being exposed through the media."

Lauren Spierer, 20, was last seen at her Bloomington apartment last June 3.

"If you have written an anonymous letter and feel you now have the courage to come forward, I beg you to do so. What we want more than anything is to show Lauren the respect she deserves by bringing her home," Charlene Spierer wrote. "Hasn't she already paid for her mistakes with the ultimate sacrifice? Please…anything small could be big."